For the sake of better understanding of a prior art swash plate type compressor to which the present invention is relevant, reference is had to FIGS. 8 and 9 of the drawings accompanying herewith, showing a piston 92 and its position relative to a swash plate 90, respectively, in the prior art swash plate type refrigerant compressor incorporated in an automotive air conditioning system. The piston 92 has a pair of head portions 92a at its opposite ends connected integrally by its intermediate neck portion 92b, as shown in FIG. 8, and fitted slidably in a cylinder bore 91, as shown in FIG. 9. In operation, the swash plate 90 is driven to rotate in the arrow direction designated by symbol P, making a wobbling movement so as to impart a reciprocating motion to the piston 92 by way of conventional shoes 93 (only one being shown) interposed between the opposite inclined surfaces of the swash plate 90 and the inner ends of the piston heads 92a, respectively.
As shown clearly in FIG. 9, the neck portion 92b of the piston 92 has a pair of surfaces 92c which are formed with such an inclination that each of such surfaces substantially conform to the curvature of the circumferential peripheral surface 90a of the circular swash plate 90 in confrontation therewith with a clearance C provided between such inclined surface 92c and the swash plate peripheral surface 90a. Thus, the axial rotation of the piston 92 is regulated. However, such a swash plate type compressor poses a problem as will be described below.
In general, the piston 92 is susceptible to the movement in arrow direction R under the influence of the rotation of the swash plate 90 which is transmitted via the shoe 93 to the piston, thereby the piston 92 being caused to move a slight distance allowed by the afore-mentioned clearance C until the inclined surface 92c on the side downstream with respect to the direction R is brought into contact with the swash plate peripheral surface 90a.
In the early period of a suction stroke, or just after the completion of a compression stroke, of one piston head 92a of the double-headed piston 92, the pressure in the cylinder bore 91 is relatively low and, therefore, there is a tendency of the piston 92 making the slight movements in the arrow direction R and counter arrow direction alternately while allowing its inclined surfaces 92c to be rebounded by the peripheral surface 90a of the swash plate 90 which is rotated with a high magnitude of kinetic energy.
Both inclined surfaces 92c of the piston 92 thus hit against the swash plate peripheral surface 90a alternately, causing not only continuous impact noise but also harmful wear on the inclined surfaces 92c of the piston and/or the swash plate peripheral surface 90a.
On the other hand, in the later period of a compression stroke, when the piston head 92a approaches its top dead center and, therefore, a high pressure prevails in the cylinder bore 91, the piston 92 tends to be held in its slightly rotated position without rebounding, with one surface 92c of the piston 92, or the surface on the right-hand side as viewed in FIG. 9, placed in strong pressing contact with the circumferential peripheral surface 90a of the rotating swash plate 90. Thus, the swash plate peripheral surface 90a is subjected to the scratching action by the edge of the inclined surface 92c of the piston 90 which may cause damage to the swash plate surface 90a.